FReplace battert (duh!) and maybe reset.
RTFM
https://drive.google.com/viewerng/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnwxNmJsZWFzZGFsZWF2ZW51ZXxneDo3NWNhMGE2NDA0ZDdlZTc1
http://www.scribd.com/doc/79441977/BOSS-Therm-Programmable-Room-Thermostat-User-Instructions-BPS242RF#scribd
http://fixed4free.com/answers.php?id=309560
and if that's the wrong one just blame yourself for deciding not to tell us the model number
XXX
December 2015